How to connect dots where there are missing values?

Question

lets take this example:

       test=c(1,5,NA,5,4,1,NA,3,3,5,4,2)

      plot(test,type=\"l\")

This will plot test but will not connect the

Answer 1

Another way that preserves the missing value in the same spots

data=data.frame(x=1:12,y=test)
plot(data)
lines(data)
lines(na.omit(data),col=2)

Or in ggplot2

ggplot(data,aes(x,y))+geom_point()+geom_line(data=na.omit(data))

Answer 2

There isn't a way to ignore the missing values. You need to replace them with interpolated values.

# using base packages only
plot(approx(test, xout=seq_along(test))$y, type="l")
# or, using zoo
library(zoo)
plot(na.approx(test), type="l")

Answer 3

One options is:

plot(na.omit(test), type = "l")

If you want to retain the x-axis going from 1 - length(test) then:

plot(na.omit(cbind(x = seq_along(test), y = test)), type = "l")

Answer 4

Either you have to ignore the NAs with the mentioned solutions using na.omit() or you try to replace the NAs with reasonable values - you can use the package imputeTS for this.

You could e.g. interpolate:

library(imputeTS)
imp <- na.interpolation(test)
plot(imp, type="l")

You could take the mean as replacement:

library(imputeTS)
imp <- na.mean(test)
plot(imp, type="l")

You could also take the moving average as replacment:

library(imputeTS)
imp <- na.ma(test)
plot(imp, type="l")

In the end, it makes sense to use what is best for your use case. Oftentimes this will be 'ignoring' the NAs - since interpolation/imputation is only a estimation of the real values and also requires selecting the right method.